1. Field of the Invention
This invention relates to a hydraulic damper device, more particularly to a hydraulic damper device for retarding movement of a movable member, such as a door or a drawer toward a stationary member, such as a framework or a furniture article.
2. Description of the Related Art
As illustrated in FIGS. 1 to 3, a conventional hydraulic damper device, which is provided for connecting a movable member (not shown), such as a door or a drawer, to a stationary member (not shown), such as a framework, and for retarding movement of the movable member toward and away from the stationary member, generally includes a cylinder unit 11 and a piston unit 13. The cylinder unit 11 includes a cylinder body 10 and a plug 12 that is disposed slidably in and cooperates with the cylinder body 10 to define a liquid chamber 110, which is adapted to receive a hydraulic liquid therein. The piston unit 13 includes a piston 131, a piston rod 132 that extends through the plug 12 into the liquid chamber 110 to connect with the piston 131, and an elastic deformable annular valve member 133. The piston 131 is disposed in the liquid chamber 110 to divide the liquid chamber 100 into first and second compartments 111, 113, and includes first and second annular segments 101, 102 and an annular middle segment 103 that is disposed between the first and second annular segments 101, 102 and that cooperates with the first and second annular segments 101, 102 to define an annular groove 136 thereamong. The piston 131 defines a fluid passage 130 that extends through the first and second annular segments 101, 102 and the middle segment 103. The first and second annular segments 101, 102 cooperate with an inner surface 115 of the cylinder body 10 to define first and second gaps 134, 135, respectively. The fluid passage 130 cooperates with an upper section 1341 of the first gap 134 to define a first fluid path (P1) (see FIG. 2) for fluid communication between the first and second compartments 111, 113. The second gap 135 cooperates with the annular groove 136 and the first gap 134 to define a second fluid path (P2) (see FIG. 3) for fluid communication between the first and second compartments 111, 113. The annular valve member 133 is disposed movably in the annular groove 136, and is driven by the hydraulic liquid through axial movement of the piston 131 to move relative to the piston 131 between a closing position (see FIG. 2) and an opening position (see FIG. 3). In the closing position, the annular valve member 133 is deformed and abuts against the first annular segment 101, the middle segment 103 and the inner surface 115 of the cylinder body 10 so as to close a lower section 1342 of the first gap 134, so that fluid communication between the first and second compartments 111, 113 is permitted through the first fluid path (P1) and is prevented through the second fluid path (P2). In the opening position, the annular valve member 131 rests on the second annular segment 102, and is away from the lower section 1342 of the first gap 134, so that fluid communication between the first and second compartments 111, 113 is permitted through the first and second fluid paths (P1, P2).
It is noted that the inner surface 115 of the cylinder body 10 is cylindrical in shape and that the annular middle segment 103 has a cylindrical outer surface 138. As such, the annular groove 136 has a constant radial width (W) along an axial length thereof. Since the annular valve member 133 is pressed against an end face 139 of the first annular segment 101 and is deformed by the hydraulic liquid when the annular valve member 133 is moved by the hydraulic liquid from the opening position to the closing position as a result of movement of the piston 131 away from the plug 12, the annular valve member 133 is undesirably clamped tightly between the inner surface 115 and the cylindrical outer surface 138. As such, the resistance to movement of the annular valve member 133 from the closing position toward the opening position is considerably increased, and a longer time is required to release the annular valve member 133 from the clamping action and to permit the annular valve member 133 to return to its original shape (i.e., non-deformed shape).